public static class ListExt
{
    public static void AddSorted<T>(this List<T> @this, T item) where T: IComparable<T>
    {
        if (@this.Count == 0)
        {
            @this.Add(item);
            return;
        }
        if (@this[@this.Count-1].CompareTo(item) <= 0)
        {
            @this.Add(item);
            return;
        }
        if (@this[0].CompareTo(item) >= 0)
        {
            @this.Insert(0, item);
            return;
        }
        int index = @this.BinarySearch(item);
        if (index < 0) 
            index = ~index;
        @this.Insert(index, item);
    }
}